1. Field of the Invention
The present invention relates to a sheet processing apparatus capable of binding a sheet bundle and an image forming apparatus including the same.
2. Description of the Related Art
Heretofore, there is known an image forming apparatus such as a copier, a printer, a facsimile, and a multi-function printer including a sheet processing apparatus configured to bind a plurality of sheets (sheet bundle) on which images have been formed. Many of the sheet processing apparatuses provided in the image forming apparatus is configured to bind a sheet bundle by using metallic staples. It is because the sheet processing apparatus using the metallic staples can bind the sheet bundle securely at a positioned specified by a user.
However, the sheet bundle bound by the metallic staples necessitates the staples to be removed from the sheet bundle in putting through a shredder or in recycling the sheets. It is a cumbersome work to remove the staples from the sheet bundle, and the removed staples become waste, so that it is costly to use staples as a whole. Then, lately, there is proposed a sheet processing apparatus configured to bind sheets by entangling fibers of the sheets by forming convexities and concavities in a direction of a thickness of the sheet bundle and by joining the sheets with each other (referred to as ‘staple-less biding’ hereinafter) as disclosed in Japanese Patent Application Laid-open NO. 2010-189101.
Here, the sheet processing apparatus described in Japanese Patent Application Laid-open No. 2010-189101 is configured to form the convexities and concavities on the sheet bundle by a pair of tooth-shaped members having upper and lower teeth and to release the bound sheet bundle by moving the upper and lower teeth in directions separating from each other by a compression spring. Therefore, there is a possibility that either one of the upper and lower teeth bites into the sheet, and the sheet may stick to the teeth if an engagement force of the upper and lower teeth is increased. It is because the sheet bundle bites into the teeth and a wedge condition is brought about as the fibers of the compressed sheets get into fine cut steps formed in creating the teeth.
Here, in a case where the bounded sheet bundle is tried to be conveyed by pushing an end portion thereof by a press member, the sheet bundle deflects between a part biting with either one of the upper and lower teeth and the part pressed by a press member. Then, while the sheet bundle is peeled off from either one of the upper and lower teeth and starts to move by being pushed by the press member, there is a possibility that the sheet bundle jumps out as the deflection caused in the sheet bundle is released at once.